Short RNA duplexes have been shown to be the effective guides that mediate RNA interference in many in vitro and in vivo models (Hamilton et al. 1999, Zamore et al., 2000, Caplen et al., 2001, Elbashir et al., 2001, Yang et al., 2000).
Most commonly, synthetic siRNA duplexes are designed such as a stretch of 19 contiguous ribonucleotide base-pairs is flanked with 2-3 unpaired nucleotides at the 3′-end of each strand (“overhangs”). This 21-nt siRNA species has been found to be generated during DICER-mediated cleavage of long ds-RNA in mammalian and non-mammalian systems (Bernstein et al., 2001, Ketting et al., 2001). This particular 21-mer siRNA format has been firstly selected from a drosophila melanogaster model and then highlighted regarding its efficiency (Elbashir et al. 2001). Consequently, the major part of today's studies applying synthetic siRNAs as gene inhibitors is relying on this “Wildtype” 21-mer siRNA derivative. For the overhangs usually 2′-deoxynucleotides are used, notably for cost reasons but also with regard to a potential-protection against intracellular nuclease activity.
The present invention now provides a new and inventive format for double-stranded RNA (“dsRNA”) mediating RNAi. The blunt-ended siRNAs in accordance with the present invention overcome disadvantages of the synthetic siRNAs with 3′-overhangs which are currently used in the art.